Doc Brown's Chemistry  Revising Organic Chemistry

The Molecular Structure and Nomenclature (naming) of the homologous series of ALCOHOLS of general formula C_nH_2n+1OH (and some isomeric ethers) Part 1

Examples of displayed formula of alcohol and ether molecules, graphic formula, molecular formula, skeletal formula, structural formula of this homologous series

including isomers of molecular formula up to C₇H₁₆O, lower ETHER (alkoxyalkanes) functional group isomers and epoxyalkanes

Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE Chemistry revising courses for pre-university students (equal to US grade 11 and grade 12 and Honours/honors level courses)

Examples of 1b chloroalcohols, 2. Diols/triols, 3. Cyclo-alcohols, 4. Phenols, 5. Epoxy compounds

organic chemical id tests * Summary of functional groups * EMAIL query?comment

 m/c quiz naming alcohols/ethers * type in name quiz on alcohols/ethers

• Alcohols have the hydroxy group OH attached to at least one of the carbon atoms in the chain. If the OH group is directly attached to a benzene ring , it is classified as a phenol.
• The primary suffix name is ..ol for alcohol and so for the longest carbon chain (alkanol) the names are based on: 1 carbon, methanol; 2 carbons, ethanol; 3 carbons, propanol; 4 carbons, butanol. After these 4 preserved 'old trivial' names, the name is 'numerically' systematic e.g. 5 carbons, pentanol; 6 hexanol, 7 heptanol, 8 octanol etc.
• The positions of the substituent alkyl (or other) groups are denoted by using the lowest possible numbers for the associated carbon atoms in the main chain.
• If there is more than one 'type' of substituent e.g. using the prefixes: methyl… and ethyl.. etc., they are written out in alphabetical order (di, tri are ignored in using this rule).
• Alcohols are classified according to the atoms/groups attached to the carbon of the hydroxy group
  • Primary alcohols ('prim') have the structure R-CH₂-OH, R = H, alkyl, aryl etc. i.e. apart from methanol they have one alkyl/aryl group attached to the C of the C-OH group and 2 (3 in case of methanol only) H's attached to the C of the C-OH functional group.
  • Secondary alcohols ('sec') have the structure R₂CH-OH, R = alkyl or aryl etc. i.e. they have two alkyl/aryl groups attached to the C of the C-OH group and 1 H attached to the C of the C-OH functional group.
  • Tertiary alcohols ('tert') have the structure R₃C-OH, R = alkyl or aryl etc. i.e. they have three alkyl/aryl groups attached to the C of the C-OH group and no H attached to the C of the C-OH functional group.
• Ethers are named on the basis of the longest carbon chain with the O-R or alkoxy group, e.g. methoxy CH₃O- or ethoxy CH₃CH₂O- etc. treated as a substituent group.
• Diol and triol structures are named on the basis of the longest carbon chain and the suffix 'ol'. Diol and triol means two or three hydroxy groups in the molecule. The positions of the OH groups is denoted with the lowest possible numbers. The prefix uses the full parent alkane name e.g. butane…. Examples of diols and triols
• Cycloalcohols (cycloalkanols) are named on the basis of the number of carbon atoms in the ring (minimum 3) and the prefix 'cyclo' and the suffix 'ol' The prefix alkane name e.g. 'prop' has an 'a' added but leaves out the end 'ne' if more than one OH group (note in mono-hydroxy alcohols its propan… and in diols/triols etc. it is propane…) Examples of cyclic alcohols
• If the OH group (hydroxy) is directly attached to a benzene ring, the molecule is classified as a 'phenol'. If not, the molecule is classified as an aliphatic alcohol (e.g. all the previous examples so far!). This difference is illustrated below with molecules containing a benzene ring. Comparison of aliphatic alcohol and phenol structures
• Epoxy compounds have a -C-C-O- triangle (epoxide/oxirane ring) in their structure which is equivalent to the simplest cyclic ether. Examples of epoxy compounds
• Some 'old' names are quoted in () though their use should be avoided if possible [but many still used - just put one into GOGGLE!].

• The shapes and bond angles of simple molecules - section on bond angles in organic molecules

1a Aliphatic alcohols C_nH_2n+1OH (and isomeric ethers)

(1) The simplest alcohol is methanol (prim) (methyl alcohol), molecular formula of (a)

and four structural formulae representations:

(b)  (c) d) and (d),

the latter gives a 3-dimensional structural formula impression of the molecule.

NOTES:

(1) all the C-C-H, H-C-H, C-O-H, C-C-O or H-C-O bond angles are all approximately 109 degrees in all the non-cyclic alcohols or alkanols shown here or below.

(2) From (b), the most 'shortened' structural formula, to (d), the most detailed structural formula, show increasing detail of the specific bonds and spatial arrangement of the atoms. (3)The naming of alcohols is based on the longest carbon chain and the suffix 'ol' meaning the functional group -OH (hydroxyl) attached to the carbon chain.

(2) The next alcohol is ethanol (prim) (ethyl alcohol, 'alcohol'), molecular formula (a),

five structural formulae representations

(b), (c), (d), (e) and (f) and the skeletal formula is (g).

NOTE: The skeletal formula is that of ethane plus the -OH, so the bond between the carbon chain and the hydroxyl group is shown in the skeletal formula - do NOT confuse it with a 'propane skeleton' - watch out for this in alcohols, ethers and any other structures where a H atom is replaced by a group that is NOT alkyl. The skeletal formula usually represents the bond network /\/ etc. apart from the C-H bonds.

(3) With the molecular formula (a), we have the first ether isomer of an alcohol. Methoxymethane (dimethyl ether) has the structural formulae (b), (c), (d), (e), (f) , NOTE(1) The H-C-O or C-O-C bond angles are all approximately 109 degrees (see notes for methanol at the start). (2)Ethers are named on the basis of (I) the longest carbon chain, and (II) the -OR group (where R is alkyl), is treated as a substituent in the longest carbon chain (better illustrated with later examples). The -OR or alkoxy group is named after its carbon length e.g. 'meth', 'eth' etc. plus an added suffix of 'oxy'.

There are two structural (position) isomers of alcohols/alkanols of molecular formula , molecules (4) and (5)

(4) Propan-1-ol (prim) (1-propanol, n-propanol, n-propyl alcohol) has the structural formulae

(a), (b), (c)

or (d) and the skeletal formula is (e).

NOTE a suffix number is now needed to show the position of the -OH or 'ol' functional group.

(5) Propan-2-ol (sec) (2-propanol, isopropanol, isopropyl alcohol) has the structural formulae

(a), (b), (c),

(d) the skeletal formula is (e)

(6) There is one ether functional group structural isomer with the molecular formula

(a). This is methoxyethane whose structural formulae are

(b), (c), (d),

(e) and the skeletal formula is (f)

There are four structural isomers of which are alcohols. Molecules (7) to (10)

(7) Butan-1-ol (prim) (1-butanol, n-butanol, n-butyl alcohol), shortened structural formulae

(a) or (b)

and the skeletal formula is (c)

(8) Butan-2-ol (sec) (2-butanol, sec-butyl alcohol, shortened structural formulae (a)

or (b) and the skeletal formula is (c)

(9) 2-methylpropan-1-ol (sec) (isobutyl alcohol, isobutanol), shortened structural formulae

(a) or (b) and the skeletal formula is (c)

(10) 2-methylpropan-2-ol (tert) (tert-butyl alcohol), shortened structural formulae (a)

or (b) and the skeletal formula is (c)

There are three isomeric ethers, isomeric with the alcohols of molecular formula (11) to (13)

(11) ethoxyethane (diethyl ether, 'ether'), structural formulae (a), (b), (c) or (d) and the skeletal formula is (e)

(12) 1-methoxypropane (use of prefix number now required), shortened structural formulae (a) or (b) and the skeletal formula is (c)

(13) 2-methoxypropane, shortened structural formula (a) or (b) and the skeletal formula is (c)

There are 8 isomeric alcohols derived from the molecular formula (14) to (21)

(14) pentan-1-ol (1-pentanol, n-pentanol, n-pentyl alcohol, n-amyl alcohol), , shortened structural formula (a) or (b) and the skeletal formula is (c)

(15) pentan-2-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(16) pentan-3-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(17) 2-methylbutan-1-ol ('active' amyl alcohol), shortened structural formula (a) or (b) and the skeletal formula is (c) NOTE from now on you will notice that the lowest number is for the 'highest ranking' substituent in the main carbon chain i.e. 'ol' ranks higher than 'methyl' and uses the lowest available number first.

(18) 3-methylbutan-1-ol (isopentanol, isoamyl alcohol), shortened structural formula (a) or (b) and the skeletal formula is (c)

(19) 2-methylbutan-2-ol (t-amyl alcohol, t-pentanol), shortened structural formula (a) or (b) and the skeletal formula is (c)

(20) 3-methylbutan-2-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(21) 2,2-dimethylpropan-1-ol (neopentyl alcohol), shortened structural formula (a) or (b) and the skeletal formula is (c)

There are 6 isomeric ethers, also isomeric with the above 8 alcohols derived from the molecular formula (22) to (27)

(22) 1-methoxybutane, shortened structural formula (a) or (b) and the skeletal formula is (c)

(23) 2-methoxybutane, shortened structural formula (a) or (b) and the skeletal formula is (c)

(24) 1-ethoxypropane, shortened structural formula (a) or (b) and the skeletal formula is (c)

(25) 2-ethoxypropane, shortened structural formula (a) or (b) and the skeletal formula is (c)

(26) 1-methoxy-2-methylpropane, shortened structural formula (a) or (b) and the skeletal formula is (c)

(27) 2-methoxy-2-methylpropane, shortened structural formula (a) or (b) and the skeletal formula is (c)

There are 17 isomeric alcohols derived from the molecular formula (28) to (44), ethers excluded for the moment!

(28) hexan-1-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(29) hexan-2-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(30) hexan-3-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(31) 2-methylpentan-1-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(32) 3-methylpentan-1-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(33) 4-methylpentan-1-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(34) 2-methylpentan-2-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(35) 3-methylpentan-2-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(36) 4-methylpentan-2-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(37) 2-methylpentan-3-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(38) 3-methylpentan-3-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(39) 2,2-dimethylbutan-1-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(40) 2,3-dimethylbutan-1-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(41) 3,3-dimethylbutan-1-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(42) 2,3-dimethylbutan-2-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(43) 3,3-dimethylbutan-2-ol, shortened structural formula (a) or (b) and the skeletal formula is (c)

(44) 2-ethylbutan-1-ol (name does not fit in with longest carbon chain rule, but a logical name to use), shortened structural formula (a) or (b) and the skeletal formula is (c)

1b Examples of aliphatic 'chloroalcohols'

1. chloroethanol or 2-chloroethanol  (1. based on C₂H₅OCl)

2. 2-chloropropan-1-ol  (2. to 4.  based on isomers of C₃H₇OCl)

3. 3-chloropropan-1-ol

4. 1-chloropropan-2-ol

5. 2-chlorobutan-1-ol  (5. to 13.  based on isomers of C₄H₉OCl)

6. 3-chlorobutan-1-ol

7. 4-chlorobutan-1-ol

8. 1-chlorobutan-2-ol

9. 3-chlorobutan-2-ol

10. 4-chlorobutan-2-ol

11. 1-chloro-2-methylpropan-2-ol

12. 2-chloro-2-methylpropan-1-ol

13. 3-chloro-2-methylpropan-1-ol

Copyright Dr W P Brown 2000-2010 All rights reserved on the revision notes pages, quizzes, worksheets, x-words etc.